1. Field of the Invention
The present invention relates to a fire alarm system and to a smoke and flame detector for use in a fire alarm system.
2. Description of the Prior Art
Heretofore, two methods have been principally used in the detection of smoke. The first method utilizes a light beam and a photosensitive cell and the other utilizes an ionization source. In the system using a light beam, the beam is directed onto the photocell and should smoke interfere with the transmission of light then the output of the photocell will drop indicating the presence of smoke. In the ionization type detector, a radioactive source is utilized to ionize the particles constituting the smoke. The ionized particles are deflected by an electric field onto electrodes the current through which indicates the presence or absence of smoke.
Both of these systems have disadvantages. The system utilizing a light beam requires accurate alignment of the beam with the photocell. Furthermore, a physical object can interrupt the light path accidentally resulting in a false alarm. Additionally the current consumption of the light is excessive for many applications.
The ionization type detector suffers from the disadvantage that it is known to be affected by external radio fields and furthermore because it includes a radioactive source it presents a danger to health. Even if such danger is not pronounced, the presence of the radioactive source in the ionization type detector makes this detector uninviting to the public. Furthermore, ionization detectors are not sensitive to smoke emitted by burning polystyrene.